The proposed experiments will make use of the specificity of antitubulin drugs, such as colchicine and vinblastine, to study the organization of tubulin in dividing and nondividing cells, and in normal and transformed cells in culture. The existence of nonmicrotubular aggregates of tubulin in a transformed rat cell line (442 cells) and in nondividing surf clam eggs will be investigated by studying the action of various antitubulin on their structure. This will be done by isolating these structures by centrifugation and then determining the content of tubulin by a new gel electrophoresis technique. The gel electrophoresis procedure will use both urea and SDS gel electrophoresis to obtain optimum resolution of proteins. In order to interpret the response of tubulin in different cells to different antitubulins a systematic study of the effects of these drugs in vitro will be done. This study will use analytical ultracentrifugation to determine the state of aggregation of tubulin under different conditions with and with out treatment with antitubulin drugs. Dose response curves will be determined by quantitative procedures in vitro and in vivo. The in vitro analysis will be done using turbidity to measure microtubule content or by direct electron microscopic analysis where necessary. Differences in the tubulin response to drugs will be used as the basis for further investigations into the state of tubulin in cells. These experiments will consist of examining the extent of tyrosylation and phosphorylation of tubulin aggregates not effected by an antitubulin compound. From these experiments we hope to demonstrate the reality of nonmicrotubular aggregates of tubulin and to obtain data on the effects of different antitubulin on different cells. These results may help explain the basis of action of anticancer drugs such as vinblastine.